This invention relates to liquid-measuring apparatus.
This invention is concerned in particular, though not exclusively, with apparatus for providing a measure of the quantity of urine, or other body fluid, drained from a person under medical observation.
Measurement of the quantity, or rate, of drainage of urine from a patient is frequently necessary in the case of burn injury or following surgery. Conventionally, the measurement is made by feeding the urine via a catheter from the patient's bladder directly into a large-capacity container in the form of a bottle or bag. The accuracy with which such a container, a bag especially, can be calibrated and graduated to enable a direct reading of quantity to be made is limited by both practical and economic considerations. Accordingly it is usually the practice, where any sensible degree of accuracy is required, to drain the urine from the patient into a finely-graduated burette. Owing to the small capacity of the burette it is necessary to monitor its content closely and to empty it frequently. The burette is emptied, either through a tap at the bottom or by tipping it, whenever the urine reaches an upper measurement level, and the overall measurement is obtained by totalization of successive readings logged from the burette at these times. Concern with this procedure imposes a burden on the nurse or other medical attendant, and is wasteful of time. Furthermore the necessary logging and subsequent totalization of the readings is very much open to human error.
Liquid-measuring apparatus that may be used to avoid these disadvantages is disclosed in my earlier U.S. Pat. No. 3,888,126, issued June 10, 1975. With the particular form of apparatus described in that patent, a catheter from the patient's bladder feeds the urine directly into a first chamber which is provided in the form of a graduated measuring cylinder. An outlet at the bottom of the cylinder is connected by a tube to a non-return valve in the top of a transparent, flexible bag which forms a second, larger-capacity chamber of the apparatus. The tube, which provides a passageway intercoupling the two chambers, extends firstly upwardly from the outlet from the cylinder and then downwardly, around an inverted U-shaped bend, to the bag. There is no transfer of urine to the bag until it rises in the cylinder to the level of the inverted U-shaped bend, whereupon an automatic siphoning action comes into effect to drain the cylinder. The quantity transferred is the same every time and is, in the particular example described, a unit quantity of 100 c.c. The bag, which has a capacity much greater than that of the cylinder, is graduated in units of 100 c.c.
The successive steps of accumulating the urine in the cylinder and then transferring it automatically in the unit quantity to the bag proceeds as a continuous process, and the total quantity of urine drained from the patient, or the rate of such drainage, can be readily monitored, in units of 100 c.c., from the graduations of the bag. The cylinder is graduated in terms of 1 c.c. units so that an accurate measurement of the total quantity of urine involved can be derived from a `fine` reading taken against the graduations of the cylinder, and a `coarse` reading taken against the graduations of the bag.
The apparatus described in my earlier, above-mentioned patent has the advantage that it avoids the need for accurate calibration and fine graduation of a container capable of holding the full volume of liquid that is to be involved in the measurement. The calibration and graduation of the relevant container -- the bag or second chamber -- need only be to an accuracy that will enable discrimination of reading to be made between quantities that differ from one another by the transfer-quantity unit (e.g. 100 c.c.). Accuracy of measurement in this case is achieved by the transfer to the second chamber of liquid only in the unit quantity defined in relation to the smaller, and therefore more-readily calibrated, cylinder or first chamber. Furthermore, measurement to any fraction of the defined unit can be readily accommodated by providing appropriate graduation of this first chamber.